1. Field of the Invention
The present invention relates to an image processing apparatus and a method of the same for adjusting the saturation of an input image in a display system.
2. Description of the Prior Art
In current displays, all users can adjust color saturations via an On Screen Display for enhancing displaying effects of images. Referring to FIG. 1 through FIG. 2B, FIG. 1 is a functional block diagram of an image processing apparatus 1 according to prior art; FIG. 2A is a schematic diagram of the lightness gain look-up table 160a shown in FIG. 1, and FIG. 2B is a schematic diagram of the hue gain look-up table 160b shown in FIG. 1. The image processing apparatus 1 includes a first color space converter 10, a hue converter 12, a first saturation converter 14, processing units 16a and 16b, multipliers 18a and 18b, a second saturation converter 20, and a second color space converter 22. The processing unit 16a stores a lightness gain look-up table 160a, as shown in FIG. 2A. The processing unit 16b stores a hue gain look-up table 160b, as shown in FIG. 2B.
The first color space converter 10 is used for converting an input image from RGB color space into Lab color space, wherein L is a lightness component, and a and b are respective color components. The hue converter 12 is used for converting the two color components a and b into a hue (H) of the input image, wherein the hue (H) is defined as H=tan−1(b/a). The first saturation converter 14 is used for converting the two color components a and b into a saturation (S) of the input image, wherein the saturation (S) is defined as S=√{square root over (a2+b2)}.
The processing unit 16a decides a lightness gain Gain-L in accordance with the lightness (L) of an input image and the lightness gain look-up table 160a. The processing unit 16b further decides a hue gain Gain-H in accordance with the hue of the input image and the hue gain look-up table 160b. Then, the multiplier 18a multiplies the lightness gain Gain-L by the hue gain Gain-H to generate a saturation gain Gain-S. Afterwards, the multiplier 18b multiplies the saturation gain Gain-S by the saturation of the input image to generate an adjusted saturation.
The second saturation converter 20 is used for converting the adjusted saturation into the two color components a and b, and the second color space converter 22 then converts the input image from Lab color space into RGB color space.
Referring to FIG. 3A and FIG. 3B, FIG. 3A is a schematic diagram of Lab color space, and FIG. 3B is a schematic diagram of the saturation with different lightness and hues in Lab color space. As shown in FIG. 3A, in the Lab color space, the lightness (L) is controlled by heights, the hue (H) is controlled by angles, and the saturation (S) is controlled by radii. According to the previous description, the image processing apparatus 1 of prior art uses the lightness gain Gain-L and the hue gain Gain-H, respectively, to adjust the saturation of the input image. However, as shown in FIG. 3B, when the lightness of the input image is different, the range of hue saturation of the input image is also different. Because each of the sections with different lightness in the color space is distinct from others, and different hues (angles) have different ranges of saturation, selecting the lightness gain Gain-L in accordance with different lightness and selecting the hue gain Gain-H in accordance with different hues will cause the saturation to be uncontrollable and lead to color deviations.
Accordingly, the scope of the present invention is to provide an image processing apparatus and a method of the same to resolve the problems described above.